FIG. 17 is a front elevation explaining a conventional method for manufacturing a rotor coil of a rotary electric machine such as that described in Japanese Patent Laid-Open No. HEI 6-181139 (Gazette), for example.
In this conventional method for manufacturing a rotor coil, as shown in FIG. 17, a bobbin 1 in which a pair of flanges 1b are formed at two ends of a drum portion 1a is mounted to a spindle 2 and rotated as indicated by the arrow. Then, a wire material 4 is paid out through a nozzle 3 and wound onto the drum portion 1a of the rotating bobbin 1. Here, the rotor coil is obtained by reciprocating the nozzle 3 in the direction of the arrows such that the wire material 4 is arranged in rows and wound into multiple layers on the drum portion 1a. 
However, in conventional methods for manufacturing rotor coils, no consideration has been given to relationships between axial dimensions of the drum portion 1a and a diameter of the wire material 4, positional relationships between the wire material 4 in radially-adjacent layers, etc. Thus, winding disturbances occur while winding the wire material 4 onto the drum portion 1a. An outside diameter of a coil field constituted by the wound wire material 4 after completion of winding becomes uneven in an axial direction of the bobbin 1 as a result of these winding disturbances. As a result, one disadvantage has been that the wire material 4 positioned at the outermost circumference of the coil field where the outside diameter is enlarged may come into contact with an inner circumferential wall surface of a pole, damaging an electrically-insulating coating on the wire material 4 and giving rise to insulation failure. Another disadvantage has been that balance of a load acting on the wire material 4 is poor as a result of the winding disturbances, giving rise to collapse of the coil field after completion of winding.